The invention disclosed in that application relates to electric arc furnace steel making systems and specifically to such systems having a ladle metallurgical furnace therein, which systems have the advantage of requiring decreased energy input per unit of steel produced compared to prior art systems. It is particularly directed to making alloy steel at a rate limited only by the maximum melting capacity of the arc furnace. In addition the invention, without modification, is adaptable to nearly every end use found in the steel industry today and particularly to producing unique, one of a kind heats of widely varying compositions in a randomized production sequence.
For example, the invention disclosed therein makes possible the production of up to four different types of steel (as distinct from grades of steel) in a single electric arc furnace system without slowdown or delay in the processing sequence of heats regardless of the number or randomized order of the different types of steel to be made in a campaign. Thus the system will produce at least non-vacuum arc remelt steel, vacuum arc remelt steel, vacuum oxygen decarburized non-vacuum arc remelt steel and vacuum oxygen decarburized vacuum arc remelt steel as well as vacuum treated ladle metallurgical furnace steel.
Now, although the process time from the charging of the electric furnace to teeming in the invention disclosed in said application is considerably shorter than the charge to teem time in conventional electric furnace steel making, the time between furnace tap to teeming is not necessarily commensurably shortened because of the added step of ladle furnace treatment; indeed, the time span may equal or even somewhat exceed the time span in conventional electric furnace steel making due to the dwell time in the ladle metallurgical furnace. Although the ladle metallurgical furnace has heat input capacity, that capacity is considerably less than the heat input capacity of the electric arc furnace. As a consequence, and particularly in connection with the larger heat sizes experienced in the system of the aforesaid application, teeming problems may arise due to the tendency of the molten steel in the teeming vessel to cool an undesirable amount in the bottom of the teeming vessel. This cooling can adversely affect the teeming stream, as by forming a semi-solid plug or glob in or above and adjacent to the teeming nozzle which can restrict the flow rate of the teem stream.
It is therefore highly desirable that the steel in the region of the teeming nozzle be just as fluid as the steel in the balance of the teeming vessel so that blockage or restricted flow through the teeming nozzle may be avoided.
A drawback to teeming systems that utilize granular material in the teeming nozzle of the teeming vessel is the possibility that at the moment the teeming stream begins the granular material may find its way into the molten metal receiving teeming receptacle and, eventually, into the final solidified product thereby causing serious cleanliness problems in the final product.
Accordingly a need exists to ensure that the teeming stream from the teeming vessel is as fluid as it can be, even in heats of over 100 tons; that is, the temperature of the molten steel in the region of the teeming nozzle should be as close to the temperature of the steel in the regions above the teeming nozzle as possible so that a restricted flow from the teeming nozzle (sometimes referred to as a hang-up) is avoided.
And as the cleanliness specifications of the final product become tightened it is more and more incumbent on the steel maker to ensure that no steel is rejected due to an undesirably high inclusion content attributable to the insulating granular material present in the teeming nozzle region, often referred to as the well block or well block region.
It is accordingly an object of the invention disclosed herein to provide, in a system having a single arc furnace, a single metallurgical furnace and a single vacuum treatment station means for ensuring that teeming stream difficulties, such as hang-ups, do not arise due to a temperature differential between the molten steel adjacent the well block in a teeming ladle and regions of the steel remote from the well block.
Another object of the invention is to decrease or eliminate the presence of undesirable inclusions in the final, solidified product attributable to the presence of granular material in the passage in the nozzle of the teeming vessel.
Like numerals will be used to refer to like or similar parts from Figure to Figure of the drawing.